Electrode foil and organic device

ABSTRACT

There are provided an electrode foil which has both the functions of a supporting base material and a reflective electrode and also has a superior thermal conductivity and heat resistance; and an organic device using the same. The electrode foil comprises a metal foil; a diffusion prevention layer for preventing diffusion of metal derived from the metal foil, the diffusion prevention layer being provided directly on the metal foil; and a reflective layer provided directly on the diffusion prevention layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2010-211189 filed on Sep. 21, 2010, the entire disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an electrode foil using a metal foil,and to an organic device using the electrode foil, such as an organic ELelement, an organic EL lighting, an organic solar cell or the like.

BACKGROUND ART

In recent years, organic EL lighting has been drawing attention as aneco-friendly green device. Features of the organic EL lightinginclude: 1) a low power consumption as compared with an incandescentlamp; 2) a thin profile and light weight; and 3) a flexibility. At themoment, the organic EL lightings are being developed so as to attain theabove features of 2) and 3). In this respect, glass substrates that havebeen conventionally used in flat panel displays (FPD) and the like areunable to attain the above features of 2) and 3).

In view of this, there are researches being conducted on a substrate asa support (hereinafter, “supporting base material”) for organic ELlighting, proposing an ultra-thin glass, a resin film, a metal foil orthe like as a possible supporting base material. The ultra-thin glass issuperior in heat resistance, barrier performance and opticaltransparency and has good flexibility, but is somewhat inferior inhandling and has low thermal conductivity and high material cost.Further, the resin film is superior in handling and flexibility and haslow material cost and good optical transparency, but is inferior in heatresistance and barrier performance and has low thermal conductivity.

In contrast, apart from the absence of optical transparency, the metalfoil has excellent features such that it is superior in heat resistance,barrier performance, handling, and thermal conductivity and also hasgood flexibility and low material cost. In particular, a typicalflexible glass or film has an extremely low thermal conductivity of 1W/m° C. or lower, while a copper foil has an extremely high thermalconductivity of around 280 W/m° C. However, in order to use the metalfoil as a supporting base material for flexible electronic devices, thesurface of the metal foil needs to be covered with an insulating film.

For instance, Patent Literature 1 (JP2007-536697A) discloses an organiclight-emitting device comprising a lower electrode layer, an organiclayer, and an upper electrode layer on a flexible substrate, describingthat a metal foil that may be covered with an insulating film can beused as the flexible substrate.

Patent Literature 2 (JP2008-142970A) discloses an insulator-coated metalfoil for flexible electronic devices, which comprises a stainless steelfoil having a surface roughness Ra of from 30 nm to 500 nm. The metalfoil, of which the surface is coated with the insulator film, is used asa supporting base material for forming thereon an electronic device,such as thin film transistor (TFT).

Patent Literature 3 (JP2001-270036A) discloses a flexible metal foillaminate comprising a metal foil having a surface roughness Ra of about0.2 μm or less and a heat-adhesive polyimide coating laminated on thesurface the metal foil.

Patent Literature 4 (JP2007-217787A) discloses an electrolytic copperfoil having a surface roughness (Rzjis) of less than 1.0 μm on thedeposition side thereof so as to attain a low profile on the surface tobe bonded to an insulator-layer constituent material. However, thesurface roughness (Rzjis) disclosed in this literature is 0.27 μm atbest.

CITATION LIST Patent Literature [Patent Literature 1] JP2007-536697A[Patent Literature 2] JP2008-142970A [Patent Literature 3]JP2001-270036A [Patent Literature 4] JP2007-217787A SUMMARY OF INVENTION

The inventors have currently found that providing a reflective layer ona metal foil enables attainment of an electrode foil useful for flexibleorganic devices, which has both the functions of a supporting basematerial and a reflective electrode and also has a superior thermalconductivity. Moreover, interposing a diffusion prevention layer, whichprevents diffusion of metal derived from the metal foil, between thereflective layer and the metal foil enables an improvement in the heatresistance of the electrode foils.

It is thus an object of the present invention to provide an electrodefoil useful for flexible organic devices, which has both the functionsof a supporting base material and a reflective electrode and also has asuperior thermal conductivity and heat resistance.

According to an aspect of the present invention, there is provided anelectrode foil comprising:

-   a metal foil;-   a diffusion prevention layer for preventing diffusion of metal    derived from the metal foil, the diffusion prevention layer being    provided directly on the metal foil; and-   a reflective layer provided directly on the diffusion prevention    layer.

According to another aspect of the present invention, there is providedan organic device which is an organic EL element and/or an organic solarcell, the organic device comprising:

-   the above electrode foil;-   an organic semiconductor layer comprising an organic EL layer and/or    an organic solar cell active layer, the organic semiconductor layer    being provided directly on an outermost surface on or to the side of    the reflective layer of the electrode foil; and-   a transparent or translucent counter electrode provided on the    organic semiconductor layer.

According to still another aspect of the present invention, there isprovided an organic EL lighting comprising the above organic device asan organic EL element.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an example ofthe electrode foil according to the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a layerstructure of an organic EL element in which the electrode foil accordingto the present invention is used as an anode.

FIG. 3 is a schematic cross-sectional view illustrating an example of atop-emission type organic EL lighting according to the presentinvention.

FIG. 4 is a schematic cross-sectional view illustrating a layerstructure of an organic EL element in which the electrode foil accordingto the present invention is used as a cathode.

FIG. 5 is a photograph showing a light-emitting appearance of an organicEL element prepared in Example 4.

FIG. 6 is a graph showing the voltage dependence of brightness measuredin Examples 4 and 5.

FIG. 7 is a graph showing the voltage dependence of current densitymeasured in Examples 4 and 5.

FIG. 8 is a graph showing the voltage dependence of brightness measuredin Example 5.

FIG. 9A is a microphotograph of a cross-section of the Cu/C/Al-alloylaminate in the electrode foil with the diffusion prevention layer(Cu/C/Al-alloy/C) prepared in Example 6 as observed by TEM.

FIG. 9B is a spectrum obtained by performing EDX analysis on point B ona cross-section of the Al-alloy layer shown in FIG. 9A.

FIG. 9C is a spectrum obtained by performing EDX analysis on point C ona cross-section of the copper foil shown in FIG. 9A.

FIG. 10A is a microphotograph of a cross-section of theCu/Cr—Ti/Al-alloy laminate in the electrode foil with the diffusionprevention layer (Cu/Cr—Ti/Al-alloy/C) prepared in Example 7 as observedby TEM.

FIG. 10B is a spectrum obtained by performing EDX analysis on point B ona cross-section of the Al-alloy layer shown in FIG. 10A.

FIG. 10C is a spectrum obtained by performing EDX analysis on point C ona cross-section of the copper foil shown in FIG. 10A.

FIG. 11A is a photograph of a cross-section of the Cu/Al-alloy laminatein the electrode foil with no diffusion prevention layer (Cu/Al-alloy/C)prepared in Example 8.

FIG. 11B is a spectrum obtained by performing EDX analysis on point B ona cross-section of the Al-alloy layer shown in FIG. 11A.

FIG. 11C is a spectrum obtained by performing EDX analysis on point C ona cross-section of the copper foil shown in FIG. 11A.

DESCRIPTION OF EMBODIMENT Electrode Foil

FIG. 1 shows a schematic cross-sectional view of an example of theelectrode foil according to the present invention. The electrode foil 10shown in FIG. 1 comprises a metal foil 12; a diffusion prevention layer13 provided directly on the metal foil; a reflective layer 14 provideddirectly on the diffusion prevention layer; and optionally a bufferlayer 15 provided directly on the reflective layer. Although theelectrode foil 10 has a four-layer structure composed of the metal foil12, the diffusion prevention layer 13, the reflective layer 14 and thebuffer layer 15, the electrode foil of the present invention is notlimited thereto but may be a three-layer structure composed of the metalfoil 12, the diffusion prevention layer 13 and the reflective layer 14.While formation of a reflective layer on a metal electrode layer isgenerally conducted in top-emission type organic EL elements, it hasbeen believed that the metal electrode layer needs to be formed on asupporting base material such as an insulator substrate. Indeed, to thebest of the inventors' knowledge, no attempt has been ever made to forma reflective layer on a metal foil that can be handled solely in itselfand then to use this metal foil as an anode or a cathode of an organicEL element. In the present invention, using the metal foil 12 not onlyas a supporting base material but also as an electrode and providing areflective layer 14 thereabove via the diffusion prevention layer 13make it possible to provide an unprecedented electrode foil whichcombines three functions as a supporting base material, an electrode anda reflective layer. The electrode foil of the present invention thusmakes it possible to dispense with a supporting base material and areflective layer that have been needed in conventional top-emission typeflexible light-emitting devices. Accordingly, the electrode foil of thepresent invention is free from an insulator layer at least on or to theside of the reflective layer, and preferably is free from an insulatorlayer at any position.

The metal foil 12 is not particularly limited as long as the metal foilis a foil-like metallic material that has a strength required for asupporting base material and electrical properties required for anelectrode. A preferred metal foil is a nonmagnetic metal foil from theview point of preventing magnetic adherence of particles produced onmachining. Examples of the nonmagnetic metal preferably include copper,aluminum, nonmagnetic stainless steel, titanium, tantalum, andmolybdenum, and more preferably copper, aluminum, and nonmagneticstainless steel. The most preferable metal foil is copper foil. Copperfoil is relatively inexpensive as well as excellent in strength,flexibility, and electrical properties.

At least one of the outermost surfaces of the electrode foil 10 ispreferably an ultra-smooth surface having an arithmetic averageroughness Ra of 10.0 nm or less, more preferably 7.0 nm or less, furtherpreferably 5.0 nm or less, most preferably 3.0 nm or less. The lowerlimit of the arithmetic average roughness Ra is not particularly limitedbut may be 0 (zero). However, considering efficiency of surfacesmoothing treatment, 0.5 nm may be considered the lower limit. Thearithmetic average roughness Ra may be measured in accordance with JIS B0601-2001 by using a commercially available surface roughness meter.

The expression “at least one of the outermost surfaces of the electrodefoil 10” denotes the surface 14 a of the reflective layer 14 in the caseof the three-layer structure or the surface 15 a of the buffer layer 15in the case of the four-layer structure. The aforementioned arithmeticaverage roughness Ra of the surface 14 a of the reflective layer 14 inthe case of the three-layer structure may be attained by providing thesurface 13 a of the diffusion prevention layer 13 and the surface 12 aof the underlying metal foil 12 for the reflective layer 14 to be formedthereon with arithmetic average roughnesses Ra in a range similar tothose mentioned above, namely, 10.0 nm or less, preferably 6.0 nm orless, more preferably 3.0 nm or less; and forming a reflective layer 14thereon. In the case of the four-layer structure, the aforementionedarithmetic average roughness Ra of surface 15 a of buffer layer 15 maybe attained by forming a buffer layer 15 on the reflective layer 14provided with an arithmetic average roughness Ra of 10.0 nm or less,preferably 6.5 nm or less, more preferably 4.0 nm or less as describedabove. The surface 15 a of the buffer layer 15 thus formed has anarithmetic average roughness Ra of 10.0 nm or less, preferably 7.0 nm orless, more preferably 5.0 nm or less. As described above, it ispreferred that the surface of a layer or foil underneath the outermostsurface be provided with an arithmetic average roughness Ra equivalentto or somewhat smaller than an arithmetic average roughness Ra to beprovided on the outermost surface. The arithmetic average roughness Raof the metal foil surface not constituting the outermost surface due tothe lamination state may be evaluated by creating a cross section fromthe metal foil surface by FIB (Focused Ion Beam) processing; andobserving the cross section with a transmission electron microscope(TEM). The arithmetic average roughness Ra of the reflective layersurface not constituting the outermost surface due to the laminationstate may be evaluated in the same way.

As far as the present inventors are aware, a metal foil (particularly, acopper foil) having the aforementioned ultra-smooth surface has not beenindustrially produced to date, nor has there been any attempt to applythe metal foil to an electrode itself of flexible electronic devices. Acopper foil with a smoothed surface is commercially available, but sucha surface smoothness level of the copper foil is not sufficient fororganic EL element electrodes in that incorporating the foil to preparean organic EL element may result in short circuit due to the unevennessand thus fails to provide light emission.

In contrast, when the arithmetic average roughness Ra of theultra-smooth surface 12 a of the metal foil 12 is extremely small tosuch an extent of preferably 10.0 nm or less, more preferably 6.0 nm orless, further preferably 3.0 nm or less, short circuit that may occurbetween the foil and a counter electrode or the like can be effectivelyprevented, even if the foil is used as an organic EL element electrode.Such an ultra-smooth surface may be attained by polishing the metal foilwith CMP (Chemical Mechanical Polishing) treatment. CMP treatment may beperformed by using a known polishing liquid and a known polishing padunder known conditions. A preferable polishing liquid may comprises oneor more of polishing granules selected from ceria, silica, alumina,zirconia, and others in an amount of from about 0.5 to about 2 wt %; anoxidizing agent such as benzotriazole (BTA); and/or an organic complexforming agent such as quinaldic acid, quinolinic acid, and nicotinicacid; a surfactant such as a cationic surfactant and an anionicsurfactant; and optionally an anticorrosive agent. A preferablepolishing pad is a pad made of urethane. The polishing conditions arenot particularly limited as pad rotation speed, work load, coating flowrate of polishing liquid may be adequately regulated. It is preferablethat the rotation speed be regulated in the range of from 20 rpm to1,000 rpm, that the work load be regulated in the range of from 100gf/cm² to 500 gf/cm², and that a coating flow rate of the polishingliquid be regulated in the range of from 20 cc/min to 200 cc/min.

The ultra-smooth surface 12 a may be attained by polishing metal foil 12using electrolytic polishing, buff polishing, chemical polishing, or acombination thereof. Chemical polishing is not particularly limited asit may be performed by adequately adjusting a chemical polishingsolution, the temperature of the chemical polishing solution, dippingtime in the chemical polishing solution, and the like. For instance,chemical polishing of copper foil may be performed by using a mixture of2-aminoethanol and ammonium chloride. The temperature of the chemicalpolishing solution is preferably room temperature, while dipping method(Dip process) is preferably used. Further, dipping time in the chemicalpolishing solution is preferred to be from 10 to 120 seconds, morepreferably from 30 to 90 seconds since long dipping time tends to resultin degradation of smoothness. The metal foil after chemical polishing ispreferred to be cleansed with running water. This smoothing treatmentcan smooth the surface having an arithmetic average roughness Ra ofabout 12 nm to have an Ra of 10.0 nm or less.

The ultra-smooth surface 12 a may also be attained by a technique suchas a method of polishing the surface of the metal foil 12 by blasting ora method of melting the surface of the metal foil 12 by laser,resistance heating, lamp heating or the like and then rapidly coolingthe surface of the metal foil 12. In the case of using, as the metalfoil 12, a platable foil made of a metal such as copper, nickel, andchromium, the ultra-smooth surface may also be attained by using atransfer method. The transfer method may be conducted in accordance withknown techniques and known conditions. For instance, the surface of anelectrode plate such as SUS and titanium is smoothed by electrolyticpolishing and buff polishing so as to be provided with an arithmeticaverage roughness Ra of 10.0 nm or less. The surface of the electrodeplate thus smoothed was plated with the material of metal foil 12, whichis peeled off from the electrode plate when a desired thickness isattained. In this way, by transferring the smoothness of the electrodeplate surface to the peeled face of the metal foil 12, an ultra-smoothsurface can be attained.

The thickness of the metal foil 12 is not particularly limited as longas the metal foil does not lose flexibility and can be handled solely initself, but may be in the range of from 1 μm to 250 μm, preferably from25 μm to 250 μm, and more preferably from 35 μm to 150 μm. With suchthickness, cutting may be performed easily by using a commerciallyavailable cutting machine. In addition, unlike glass substrates, themetal foil 12 has no problems such as crack, chip or the like, and alsohas an advantage of not easily producing particles upon cutting. Themetal foil 12 may be formed in various shapes other than tetragon, suchas circle, triangle, and polygon, and can also be cut-and-pasted toprepare a light emitting body in a three-dimensional shape such as acubic shape or a ball shape since the metal foil is capable of being cutor welded. In this case, it is preferred that a light emitting layer benot formed at a cutting or welding portion of the metal foil 12.

The ultra-smooth surface 12 a is preferably cleansed with an alkalinesolution. A known alkaline solution such as an ammonia-containingsolution, a sodium hydroxide solution, and a potassium hydroxidesolution may be used as the alkaline solution. The alkaline solution ispreferably an ammonia-containing solution, more preferably an organicalkaline solution containing ammonia, further preferably atetramethylammonium hydroxide (TMAH) solution. Preferable concentrationof the TMAH solution is from 0.1 wt % to 3.0 wt %. An example of washingdescribed above includes performing cleansing at 23° C. for one minutewith use of a 0.4% TMAH solution. A similar cleansing effect can also beattained by performing UV (Ultra Violet) treatment in combination withor in place of the alkaline solution. In addition, in the case of copperfoil and the like, it is possible to remove oxides formed on the coppersurface by using an acidic cleansing solution such as dilute sulfuricacid. An example of acid cleansing includes performing cleansing for 30seconds with dilute sulfuric acid.

Prior to the formation of the diffusion prevention layer 13, it ispreferred that particles on the ultra-smooth surface 12 a be removed.Examples of an effective method for removing the particles include asonic washing method using ultra-pure water and a dry-ice blastingmethod. The dry-ice blasting method is more effective. Dry-ice blastingmethod is a method of ejecting carbon dioxide gas compressed at highpressure through a fine nozzle and thereby blowing carbon dioxidesolidified at low temperature against the ultra-smooth surface 12 a toremove the particles. Unlike wet process, this dry-ice blasting methodcan dispense with drying process, and also has an advantage of beingable to remove organic substances. The dry-ice blasting method may beperformed by using a commercially available apparatus such as a dry-icesnow system (manufactured by AIR WATER INC.).

The diffusion prevention layer 13 is directly provided on theultra-smooth surface of the metal foil 12 a. Any films having knowncompositions and structures can be used as the diffusion preventionlayer 13 as long as it has a function of preventing diffusion of metalderived from the metal foil. As a result, even when the electrode foilis exposed to a considerably high temperature, thermal migration thatmay occur from the interface between the copper foil and thealuminum-containing reflective layer can be effectively suppressed,making it possible to prevent deterioration of the surface smoothnessand optical reflectivity caused by the thermal migration. That is, heatresistance of the electrode foil can be improved. Therefore, the aboveembodiment is particularly effective in heat treatment which isperformed at a temperature of 200° C. or higher, preferably 230° C. orhigher, and more preferably 250° C. or higher after a hole injectionlayer is coated. The diffusion prevention layer 13 may be a layerstructure composed of two or more layers.

Preferable materials for constituting the diffusion prevention layer 13include (i) high-melting metals such as Mo, Ti, Ta, Cr and W, alloys andnitrides thereof; (ii) transition metals such as Ni, Fe, Co and alloysthereof; and (iii) an conductive amorphous carbon, an conductive oxide,a magnesium alloy, and a fluoride, which can also be used for the bufferlayer. Therefore, examples of the diffusion prevention layer includelayers comprising at least one of Mo, Ti, Ta, Cr, W, Ni, Fe, Co, C, Zn,Li, Y, indium oxide, tin oxide, zinc oxide, molybdenum oxide, galliumoxide, vanadium oxide, tungsten oxide, ruthenium oxide, aluminum oxide,titanium oxide, titanium nitride, chromium nitride, tantalum nitride,NIP, Ni—Zn, LiF, MgF₂, CaF₃, NaAlF₆, and NaF₆. In addition, thesecompounds are not limited to those having stoichiometric compositions.For example, a substance such as indium oxide (In₂O₃) partially devoidof oxygen can also be used as the diffusion prevention layer. This makesit possible to effectively prevent thermal migration, while bringing themetal foil 12 into close contact with the reflective layer 14electrically and mechanically. Formation of the diffusion layer may bedone in accordance with various known methods such as sputtering method,vacuum deposition method, electroplating method, non-electrolyticplating method and the like. The thickness of the diffusion preventionlayer 13 is not limited as long as there can be achieved the effect ofpreventing diffusion of metal as required for the diffusion preventionlayer, but is preferred to be 1 nm or more, more preferably 3 nm ormore, further preferably 5 nm or more. In addition, in terms ofretaining the surface smoothness of the electrode foil, the thickness ofthe diffusion prevention layer 13 is preferred to be 200 nm or less,more preferably 100 nm or less.

The reflective layer 14 is provided directly on the ultra-smooth surfaceof the diffusion prevention layer 13 a. The reflective layer 14 ispreferred to be composed of at least one selected from the groupconsisting of aluminum, aluminum alloys, silver, and silver alloys.These materials are suitable for a reflective layer due to a highoptical reflectivity and also excellent in smoothness when being formedinto thin films. In particular, aluminum and aluminum alloys arepreferable, because they are inexpensive materials. A wide variety ofaluminum alloys and silver alloys can be adopted having conventionalalloy compositions for use as an anode or a cathode of a display devicesuch as an organic EL element. Preferred examples of the aluminum alloycompositions include Al—Ni; Al—Cu; Al—Ag; Al—Ce; Al—Zn; Al—B; Al—Ta;Al—Nd; Al—Si; Al—La; Al—Co; Al—Ge; Al—Fe; Al—Li; Al—Mg; and Al—Mn. Anyelement that can constitute these alloys may be combined arbitrarily,depending on required performances. Preferred examples of the silveralloy compositions include Ag—Pd; Ag—Cu; Ag—Al; Ag—Zn; Ag—Mg; Ag—Mn;Ag—Cr; Ag—Ti; Ag—Ta; Ag—Co; Ag—Si; Ag—Ge; Ag—Li; Ag—B; Ag—Pt; Ag—Fe;Ag—Nd; Ag—La; and Ag—Ce. Any element that can constitute these alloysmay be combined arbitrarily, depending on required performances. Thethickness of the reflective layer 13 is not particularly limited, but ispreferably from 30 nm to 500 nm, more preferably from 50 nm to 300 nm,and further preferably from 100 nm to 250 nm.

The surface 14 a of the reflective layer 14 has an arithmetic averageroughness Ra of preferably 10.0 nm or less, more preferably 6.5 nm orless, further preferably 4.0 nm or less. As described above, since thereflective layer is formed on the ultra-smooth surface of the metal foilin the present invention, it is possible to provide a small arithmeticaverage roughness Ra even on the surface of the reflective layer andthus to attain a higher smoothness. This enables reduction in risk ofshort circuit between the organic EL layers, which is caused byoccurrence of excessive unevenness. In addition, since there is no needto thickly form a hole injection layer and a hole transport layer or anelectron injection layer and an electron transport layer for eliminatingthe effect of unevenness of the reflective layer surface, these layersand an organic EL layer that includes these layers may be made thinnerthan conventional thicknesses. As a result, it is possible to reduce theusage of extremely expensive organic raw materials so as to lowerproduction cost as well as to make the organic EL layer thinner so as toimprove light-emitting efficiency.

It is preferred that the buffer layer 15 be provided directly on thereflective layer 14. The buffer layer 15 is not particularly limited aslong as it makes contact with an organic EL layer in an organic ELelement to improve hole injection efficiency or electron injectionefficiency as well as to provide a desired work function. Nonetheless,the buffer layer in the present invention is preferably transparent ortranslucent from the viewpoint of enabling the metal foil to function asa reflective layer.

The buffer layer 15 is preferably at least one selected from the groupconsisting of an conductive amorphous carbon film, an conductive oxidefilm, a magnesium alloy film, and a fluoride film, and may be selectedas needed depending on applications such as an anode or a cathode andrequired performances.

As the conductive amorphous carbon film, various kinds of amorphouscarbon films provided with electrical conductivity by regulatinghydrogen concentration or impurity concentration may be used. Formationof the conductive amorphous carbon film is preferred to be conducted bysputtering. A carbon target subjected to purification treatment isdesired to be used for the sputtering. In addition, porous carbonimpregnated with B, Si, Al and/or Cu may be used. When the conductiveamorphous carbon film is used as the buffer layer, any of an aluminumfilm, an aluminum alloy film, a silver film, and a silver alloy film maybe suitably used for the reflective layer, while aluminum alloys arepreferable in consideration of smoothness and material cost.

A preferable conductive amorphous carbon film is composed of anconductive amorphous carbon having a hydrogen concentration of 15 at %or less. The hydrogen concentration is more preferably 12 at % or lessand further preferably 5 at % or less. Although the lower limit of thehydrogen concentration is not particularly limited but may be 0 (zero),a typical lower limit may be 3 at % in consideration of unavoidablecontamination with hydrogen from film forming environment uponsputtering. The hydrogen concentration in the buffer layer may bemeasured by various known methods, among which HFS (Hydrogen ForwardScattering) is preferred. The hydrogen concentration in the conductiveamorphous carbon film is defined herein as a hydrogen concentrationobtained by measuring the amounts of carbon and hydrogen by HFS or thelike and assuming the total amount of these atoms as 100 at %. Extremelylowering the hydrogen concentration in this way makes it possible toavoid decrease in electrical conductivity or development of insulationproperties, which are caused by the carbon atoms constituting the bufferlayer being terminated with hydrogen, and thus to provide the bufferlayer with a high electrical conductivity required for an electrode.Therefore, it is preferable that the conductive amorphous carbon be notsubstantially doped with impurities other than carbon and hydrogen. Thephrase “not substantially doped” means that impurities are notintentionally added for the purpose of providing a certain function,allowing impurities unavoidably incorporated from film formingenvironment or the like during sputtering. In view of this, theconductive amorphous carbon in the present invention preferably has anoxygen concentration of from 0 wtppm to 300 wtppm, a halogen elementconcentration of from 0 wtppm to 1,000 wtppm, and a nitrogenconcentration of from 0 wtppm to 500 wtppm. The thickness of the bufferlayer 14 is not particularly limited, but preferably from 3 nm to 30 nm,more preferably from 3 nm to 15 nm, and further preferably from 5 nm to10 nm.

A preferable conductive oxide film may be composed of one or moreselected from the group consisting of InO_(N), SnO_(x), ZnO_(x),MoO_(x), GaO_(x), VO_(x), WO_(x), RuO_(x), AlO_(x), TiO_(x), andGeO_(x). Typical examples thereof include ITO (indium tin oxide) and IZO(indium zinc oxide). The conductive oxide film may be formed by using aknown technique such as sputtering and vacuum deposition, preferably DCmagnetron sputtering. The target material used for sputtering may beprepared by hot pressing or cold pressing, so that the oxides describedabove may be combined together as needed to attain desiredcharacteristics. When the conductive oxide film is used as the bufferlayer, Al—Ni alloys, Ag, and Ag alloy are particularly suitable for thereflective layer.

A preferable magnesium alloy film may be composed of an alloy comprisingMg and one or more additive selected from the group consisting of Ag,Al, Zn, Li, Y, and Ca. The magnesium alloy film may be formed by using aknown technique such as sputtering method or vacuum deposition method,preferably vacuum deposition method.

A preferable fluoride film may be composed of one or more selected fromthe group consisting of LiF, MgF₂, CaF₂, AlF₃, Na₃AlF₆, and NaF₆. Thefluoride film may be formed by using a known technique such assputtering method or vacuum deposition method, preferably vacuumdeposition method.

The surface 15 a of the buffer layer 15 has an arithmetic averageroughness Ra of 10.0 nm or less, preferably 7.0 nm or less, morepreferably 5.0 nm or less. As described above, the buffer layer isformed on the ultra-smooth surface of the reflective layer of which theultra-smoothness arises from the ultra-smooth metal foil, so that thearithmetic average roughness Ra may be reduced also on the surface ofthe buffer layer to realize a high smoothness. This makes it possible toreduce the risk of short circuit in the organic EL layer, which arisesfrom generation of excess unevenness. In addition, a hole injectionlayer and a hole transport layer or an electron injection layer and anelectron transport layer are not needed to be formed thick so as toeliminate the influence of unevenness of the buffer layer surface.Therefore, these layers and an organic EL layer that includes theselayers may be made thinner than usual. As a result, the amount ofextremely expensive organic raw materials to be used is reduced to lowerproduction cost, while the organic EL layer can be thinned to increaselight-emitting efficiency.

An oxide film (not shown in figures) may exist between the reflectivelayer 14 and the buffer layer 15. The oxide film may be formed typicallyby allowing the anode layer to be inevitably oxidized by atmosphericoxygen. The oxide film is preferred to be as thin as possible, with athickness being preferably 3.0 nm or less, more preferably 1.5 nm orless. The oxide film may be removed by etching or the like.

The electrode foil of the present invention has a thickness ofpreferably from 1 μm to 300 μm, more preferably from 25 μm to 250 μm,further preferably from 35 μm to 150 μm, most preferably from 40 μm to100 μm.

According to a preferred embodiment of the present invention, thesurface 12 b of the metal foil 12 opposite to the reflective layer 14may be roughened to a ten-point average roughness Rz of 1.0 μm or more,more preferably 2.0 μm or more, and further preferably 5.0 μm or more.The ten-point average roughness Rz may be measured in accordance withJIS B 0601-1994 with a commercially available roughness meter available.The surface may be roughened preferably by using a known technique suchas dry-ice blasting, sand blasting, wet etching, dry etching, or thelike. The unevenness provided on the roughened surface can improve heatdischarge characteristics.

The electrode foil of the present invention is metal-foil based, so thatthe electrode foil can be produced efficiently, for example, byroll-to-roll process without particularly necessitating a supportingbase material.

The electrode foil of the present invention may be used preferably as ananode or a cathode for various kinds of flexible organic devices(particularly, flexible light-emitting or power generating devices),thereby functioning as a reflective electrode. Examples of such flexibleorganic devices include organic EL elements; organic EL lighting;organic EL displays; electronic paper; thin-film solar cells; liquidcrystal displays; inorganic EL elements; inorganic EL displays; LEDlighting; and LED displays. Preferred are organic EL elements, organicEL lighting, organic EL displays, organic solar cells, anddye-sensitized solar cells. Organic EL lighting is more preferable inthat high brightness is attained in an ultra-thin form. In addition,since many of characteristics required for electrode materials oforganic solar cells are in common with those required for organic ELelements, the electrode foil of the present invention may be preferablyused as an anode or a cathode of organic solar cells. Namely,appropriate selection of the kind of an organic semiconductor layer tobe laminated on the electrode foil of the present invention inaccordance with known techniques makes it possible to construct anorganic device in any form of an organic EL element and an organic solarcell. It is also possible to form a light-emitting element and a powergenerating element simultaneously on the same electrode, and thereby tofabricate a composite device that has both functions of an organic ELelement and an organic solar cell. Furthermore, the electrode foil ofthe present invention may be used not only as an electrode of an organicEL element but also as an LED mounting board. In particular, theelectrode foil of the present invention may be preferably used as ananode or a cathode of LED lighting in that LED elements can be mountedin a closely packed manner.

Organic EL elements and Organic EL Lighting

A top-emission type organic EL element and an organic EL lighting may beconstructed by using the electrode foil of the present invention as areflective electrode.

FIG. 2 shows an example of a layer structure of a top-emission typeorganic EL element that uses the electrode foil of the present inventionas an anode. The organic EL element shown in FIG. 2 comprises an anodicelectrode foil 20 comprising a metal foil 22, a diffusion preventionlayer 23, a reflective layer 24 and a buffer layer 25; an organic ELlayer 26 provided directly on the buffer layer 25; and a cathode 28 as acounter electrode provided directly on the organic EL layer 26. It ispreferred that the buffer layer 25 be composed of a conductive amorphouscarbon film or a conductive oxide film so as to be suitable as an anode.

The organic EL layer 26 may employ various known EL layer structuresused for organic EL elements and may comprise optionally a holeinjection layer and/or a hole transport layer, a light-emitting layer,and optionally an electron transport layer and/or an electron injectionlayer in this order in the direction from the anodic electrode foil 20to the cathode 28. Any various known structures or compositions may beappropriately employed for each of the hole injection layer, the holetransport layer, the light-emitting layer, the electron transport layer,and the electron injection layer, without any particular limitation.

As described above, an organic solar cell may be constructed byreplacing the organic EL layer 26 with a known organic solar cell activelayer. In the case of an organic solar cell in which the electrode foilof the present invention is used as an anode, the solar cell can beconstructed by laminating, on a buffer layer (for instance, a carbonbuffer layer), a hole transport layer (PEDOT:PSS (30 nm)), a p-typeorganic semiconductor layer (for instance, BP (benzoporphyrin)), ani-type mixing layer (for instance, BP:PCBNB (fullerene derivative) of ann-type organic semiconductor and a p-type organic semiconductor, ann-type organic semiconductor layer (for instance, PCBM (fullerenederivative)), a buffer layer having a low work function (for instance,Mg—Ag), and a transparent electrode layer (for instance, IZO) in thisorder. Known materials may be appropriately used for each of theselayers without any particular limitation. The electrode used for organicsolar cells may have the same materials and structure as an theelectrode used for organic EL elements. The electrode foil of thepresent invention comprises a reflective layer and is thus expected toprovide an increase in power generation efficiency due to lightconfinement caused by cavity effect.

FIG. 3 shows an example of a layer structure of a top-emission typeorganic EL lighting in which an organic EL element shown in FIG. 2 isincorporated. In the organic EL lighting shown in FIG. 3, the organic ELelement is electrically connectable with a power source 30 through themetal foil 22 of the anodic electrode foil 20. On the buffer layer 25,the area that has no contact with the organic EL layer 26 is coveredwith an interlayer insulation film 29. The interlayer insulation film 29is preferred to be a Si-based insulation film formed by CVD in that thefilm has a high barrier performance against water and oxygen that causedegradation of organic layers. A SiN-based insulation film is morepreferable. A still more preferable interlayer insulation film is aSiNO-based insulation film in that the film has a small internal stressand an excellent bending performance.

On the upper side of the cathode 28, a sealing material 32 is providedas opposed to the organic EL element. The gap between the sealingmaterial 32 and the organic EL element 20 is filled with a sealing resinto form a sealing film 34. As the sealing material 32, glass or filmsmay be used. In the case of glass, the sealing material 32 may be bondeddirectly onto the sealing film 34 using a hydrophobic adhesive tape. Inthe case of films, both surfaces and end faces thereof may be coveredwith a Si-based insulating film. When a film having a high barrierperformance will be developed in future, sealing will be possiblewithout conducting coating treatment, and is expected to providesuperior mass productivity. As the sealing material 32, films arepreferable in terms of imparting flexibility. Nonetheless, a desiredperformance may be attained by using a sealing material formed bybonding a film to an extremely thin glass having a thickness of from 20μm to 100 μm.

While various known cathodes used for top-emission type organic ELelements may be used as the cathode 28 without any particular limitationas long as they are transparent or translucent due to the necessity totransmit light, those having low work functions are preferred. Examplesof preferable cathodes include conductive oxide films, magnesium alloyfilms, and fluoride films. A combination of two or more thereof is morepreferable. For these films, films similar to those described withregard to the buffer layer of the electrode foil may be used.

A particularly preferable cathode has a two-layer structure in which atranslucent metal layer as a buffer layer composed of a magnesium alloyfilm and/or a fluoride film is laminated onto a transparent oxide layeras a cathode layer composed of an conductive oxide film, being highlyuseful from the viewpoint of resistance as well. In this case, a highoptical transparency and a low work function are provided by bringingthe translucent metal layer (buffer layer) of the cathode 28 intocontact with the organic EL layer 26, thereby enhancing brightness andpower efficiency of the organic EL element. A most preferable example isa cathode structure formed by laminating a transparent oxide layer(cathode layer) composed of IZO (indium zinc oxide) and a translucentmetal layer (buffer layer) composed of Mg—Ag. In addition, the cathodestructure may have two or more transparent oxide layers and/or two ormore translucent metal layers. Thus, the light generated in the organicEL layer 26 passes through the cathode 28, the sealing film 34, and thesealing material 32, and is then emitted outside.

On the back side of the electrode foil 20, an auxiliary substrate may beappropriately provided depending on type of usage. The portion does notaffect light emission performance, so that materials may be selectedwith a high degree of freedom. For instance, a resin film such aspolyethylene terephthalate (PET), polyimide (PI), polycarbonate (PC),polyethersulfone (PES), and polyethernitrile (PEN) may be optimally usedbecause flexibility is not impaired.

FIG. 4 shows an example of a layer structure of a top-emission typeorganic EL element in which the electrode foil of the present inventionis used as a cathode. The organic EL element shown in FIG. 4 comprises acathodic electrode foil 40 comprising a metal foil 42, a diffusionprevention layer 43, a reflective layer 44 and a buffer layer 45; anorganic EL layer 46 provided directly on the buffer layer 44; and ananode 48 as a counter electrode provided directly on the organic ELlayer 46. The organic EL layer 46 may be composed similarly to theorganic EL layer 26 shown in FIG. 2. The buffer layer 45 may be composedsimilarly to the cathode 28 shown in FIG. 2, and preferably composed ofa conductive oxide film, a magnesium alloy film, a fluoride film, or acombination of two or more thereof. More preferably, the buffer layer 45is a translucent metal layer composed of a magnesium alloy film and/or afluoride film.

Specifically, the organic EL element that uses cathodic electrode foil40 shown in FIG. 4 corresponds to a structure in which an organic ELelement using the anodic electrode foil 20 shown in FIG. 2 is modifiedby exchanging the buffer layer 25 and the cathode 28 and reversing thelamination order from the anode side to the cathode side inside theorganic EL layer 26. For instance, it is preferable that a magnesiumalloy film or a fluoride film as the buffer layer 45 of the cathodicelectrode foil 40 is formed by sputtering or vapor deposition while afilm made of conductive amorphous carbon, MoO₃, or V₂O₅ is formed as theanode 48 by vapor deposition. In particular, in the case of forming aconductive amorphous carbon film on the organic EL layer, vacuumdeposition is preferably used in order to avoid plasma damage duringsputtering.

EXAMPLES

The present invention will be further described in detail with referenceto the following examples. Although Examples 1 to 5 are categorized asreference examples as not directed to embodiments having a diffusionprevention layer, it is evident that the present invention achieves thegiven effects in light of the entire disclosure of the followingexamples and the common technical knowledge since the effect ofpreventing diffusion of metal by the diffusion prevention layers aredemonstrated in Examples 6 to 8.

Example 1 Preparation of Cu/Al-alloy/ITO Electrode Foil

As a metal foil, 64 μm thick commercially available both-side-flatelectrolytic copper foil (DFF (Dual Flat Foil), manufactured by MitsuiMining & Smelting Co., Ltd.) was prepared. The surface roughness of thecopper foil was measured with a scanning probe microscope (Nano Scope V,manufactured by Veeco Instrument Inc.) in accordance with JISB0601-2001, resulting in an arithmetic average roughness Ra of 12.20 nm.This measurement was performed in an area of 10 μm square using aTapping Mode AFM.

The copper foil was subjected to CMP (Chemical Mechanical Polishing)treatment with a polishing machine manufactured by MAT Inc. This CMPtreatment was performed by using a polishing pad having XY grooves and acolloidal silica polishing liquid under the conditions of pad rotationspeed of 30 rpm; load of 200 gf/cm²; and liquid supply rate of 100cc/min. The copper foil thus treated with CMP was subjected tomeasurement of the surface roughness of the copper foil by using thescanning probe microscope (Nano Scope V, manufactured by VeecoInstruments Inc.) in accordance with JIS B 0601-2001, resulting in anarithmetic average roughness Ra of 0.7 nm. This measurement wasperformed in an area of 10 μm square using a Tapping Mode AFM. Thethickness of the copper foil after the CMP treatment was 48 μm.

On the surface of the copper foil treated with CMP, an Al alloyreflective layer with a thickness of 150 nm was formed by sputtering.This sputtering was performed under the conditions of input power (DC)of 1,000 W (3.1 W/cm²); ultimate vacuum of lower than 5×10⁻⁵ Pa;sputtering pressure of 0.5 Pa; Ar flow rate of 100 sccm; and substratetemperature of room temperature, after mounting an aluminum alloy target(203.2 mm diameter and 8 mm thick) having a composition of Al-0.2B-3.2Ni(at %) in a magnetron sputtering apparatus (MSL-464, manufactured byTokki Corp.) to which a cryopump was connected.

On the surface of an aluminum alloy reflective layer thus obtained, anITO buffer layer with a thickness of 10 nm was formed by sputtering.This sputtering was performed under the conditions of input power (DC)of 300 W (0.9 W/cm²); ultimate vacuum of lower than 5×10⁻⁵ Pa;sputtering pressure of 0.35 Pa; Ar flow rate of 80 sccm; O₂ flow rate of1.9 sccm; and substrate temperature at room temperature, after mountingan ITO (In₂O₃—SnO₂) target (203.2 mm diameter and 6 mm thick) containing10 wt % of Sn in a magnetron sputtering apparatus (MSL-464, manufacturedby Tokki Corp.) to which a cryopump was connected. Film thickness wascontrolled by regulating discharging time. The surface roughness of thebuffer layer thus obtained was measured in the same manner as mentionedabove, resulting in an arithmetic average roughness Ra of 2.0 nm. Thetotal thickness of the resulting electrode foil was 48 μm.

Example 2 Preparation of Cu/Al-alloy/C Electrode Foil

An electrode foil was prepared in the same manner as in Example 1 exceptthat a carbon buffer layer with a thickness of 1.7 nm or 3.5 nm wasformed by sputtering in place of the ITO buffer layer. As a carbontarget for the sputtering, two types of carbon targets were preparedincluding a non-treated carbon target with a purity of 3N (99.9%) madefrom a carbon material (IGS743, manufactured by Tokai Carbon Co., Ltd.);and a carbon target having a purity of 5N (99.999%) made from the abovecarbon material through purification treatment with a halogen gas. Byusing each of these targets, the carbon buffer layer was formed bysputtering. This sputtering was performed under the conditions of inputpower (DC) of 250 W (0.8 W/cm²); ultimate vacuum of lower than 5×10⁻⁵Pa; sputtering pressure of 0.5 Pa; Ar flow rate of 100 sccm; andsubstrate temperature at room temperature, after mounting each carbontarget (203.2 mm diameter and 8 mm thick) in a magnetron sputteringapparatus (Multi-chamber sheet-fed-type film formation apparatusMSL-464, manufactured by Tokki Corp.) to which a cryopump was connected.Film thickness was controlled by regulating discharging time. Thesurface roughness of the buffer layer thus obtained was measured in thesame manner as in Example 1, resulting in an arithmetic averageroughness Ra of 2.45 nm. The total thickness of the resulting electrodefoil was 48 μm.

Example 3 Preparation of Cu/Ag-alloy/ITO Electrode Foil

An electrode foil having a buffer layer and a reflective layer wasprepared in the same manner as in Example 1 except that an Ag alloyreflective layer with a thickness of 150 nm was formed by sputtering inplace of the Al alloy reflective layer. This sputtering was performedunder the conditions of input power (DC) of 150 W (1.9 W/cm²); ultimatevacuum of lower than 5×10⁻⁵ Pa; sputtering pressure of 0.5 Pa; Ar flowrate of 90 sccm; and substrate temperature at room temperature, aftermounting a silver alloy target (101.6 mm diameter and 5 mm thick) havinga composition of Ag-1.0Cu-1.0Pd (at %) on a magnetron sputteringapparatus (MSL-464, manufactured by Tokki Corp.) to which a cryopump wasconnected. Film thickness was controlled by regulating discharging time.

Example 4 Fabrication of Organic EL Element

An organic EL element having a structure as shown in FIGS. 2 and 3except for the absence of a diffusion prevention layer was prepared byusing as an anode the electrode foil (Cu/Al-alloy/ITO) prepared inExample 1. At the outset, a glass plate (3 cm square and 0.5 mm thick)was put on the electrode foil 20 (5 cm square) so as to make masking,followed by formation of an interlayer insulation film 29 composed ofsilicon nitride by plasma CVD (Chemical Vapor Deposition). This plasmaCVD was performed under the conditions of film forming area of 8 inchdiameter in terms of effective area; input power (RF) of 250 W (0.8W/cm²); ultimate vacuum of lower than 5×10⁻³ Pa; sputtering pressure of80 Pa; gas flow rate of SiH₄ (diluted with H₂ to 10%):NH₃:N₂=100:10:200sccm; and substrate temperature at 250° C., using a plasma CVD apparatus(PD-2202L, manufactured by Samco Inc.) to which a mechanical boosterpump (MBP) and a rotary pump (RP) were connected. The glass was thenremoved from the electrode foil 20 to obtain an interlayer insulationfilm 29 having an opening of 3 cm square on the electrode foil.

The surface of the electrode foil having the interlayer insulation filmformed thereon was cleansed as follows. First, ultrasonic cleansing for3 minute was performed twice in a bath filled with an ultrapure water(having larger than 18.0 MΩ) being replaced with a fresh one for thesecond cleansing. Subsequently, after water was removed by usingnitrogen gas, after-curing was performed at 100° C. for 3 hours. Thesurface thus treated was cleansed by UV irradiation.

On the electrode foil thus cleansed, an organic EL layer 26, a cathode28, a sealing layer 34, and a sealing material 32 were laminated.Specifically, on the buffer layer surface of the electrode foil, a50-nm-thick hole injection layer composed of copper phthalocyanine, a40-nm-thick hole transport layer composed of4,4′-bis(N,N′-(3-tolyl)amino)-3,3′-dimethylbiphenyl (HMTPD), a30-nm-thick light emitting layer composed of a host material doped withtris(2-phenylpyridine) iridium complex (Ir(ppy)₃), a 30-nm-thickelectron transport layer composed of Alq3, a 10-nm-thick translucentlayer composed of Mg—Ag (Mg:Ag=1:9), a 100-nm-thick transparent oxidelayer composed of IZO (In—Zn—O), a 300-nm-thick passivation film(sealing layer) composed of silicon nitride, a 2,000-nm-thick adhesivelayer, and a 200-μm-thick sealing glass (sealing material) werelaminated in this order. The lamination of the sealing glass wasconducted by using a double-stick tape, which corresponds to theadhesive layer. In this way, there was obtained an organic EL elementsample as shown in FIG. 3, which was 50 mm square and 300 μm thick andhad a light-emitting area of 30 mm square. When this sample wasconnected to a power source 30 and then applied with a voltage of 5.0 V,an intense light emission as shown in FIG. 5 was observed. In addition,when the applied voltage was varied to measure the change in brightness(cd/cm²) and current density (mA/cm²), there were obtained results shownin FIGS. 6 and 7 (see the plots denoted by “ITO” in these figures). Asdescribed above, the use of the electrode foil of the present inventionenables light emission with an extremely high brightness at lowvoltages.

For comparison, when an organic EL element was prepared and applied withcurrent in the same way as described above by using a both-side-flatelectrolytic copper foil with an arithmetic average roughness Ra of12.20 nm used in Example 1, short circuit occurred between theelectrodes, failing to emit light.

Example 5 Fabrication of Organic EL Element

Three types of organic EL element samples were prepared in the same wayas in Example 4 except for using electrode foils (Cu/Al-alloy/C) havingthe following three kinds of carbon buffer layers prepared in Example 2.

-   Sample “5N-C 35 Å” is an organic EL element having a 3.5-nm-thick    carbon buffer layer formed by using a carbon target having a purity    of 5N,-   Sample “3N-C 17 Å” is an organic EL element having a 1.7-nm-thick    carbon buffer layer formed by using a carbon target having a purity    of 3N, and-   Sample “5N-C 17 Å” is an organic EL element having a 1.7-nm-thick    carbon buffer layer formed by using a carbon target having a purity    of 5N.

Each of the above samples was connected to the power source 30 as shownin FIG. 3. When the applied voltage was varied to measure the change inbrightness (cd/cm²) and current density (mA/cm²), there were obtainedresults shown in FIGS. 6 to 8. As described above, the use of theelectrode foil of the present invention enables light emission with anextremely high brightness at low voltages.

Example 6 Preparation and Heat-Resistance Evaluation of Cu/C/Al-alloy/CElectrode Foil

An electrode foil was prepared in the same manner as in Example 2 exceptthat a carbon layer was formed by sputtering as a diffusion preventionlayer between the copper foil and the Al-alloy reflective layer. Thissputtering for forming the carbon diffusion prevention layer wasperformed, as in the formation of the carbon buffer layer in Example 2,under the conditions of input power (DC) of 250 W (0.8 W/cm²); ultimatevacuum of lower than 5×10⁻⁵ Pa; sputtering pressure of 0.5 Pa; Ar flowrate of 100 sccm; and substrate temperature at room temperature, aftermounting a carbon target (203.2 mm diameter and 8 mm thick) having apurity of 5N (99.999%) in a magnetron sputtering apparatus(Multi-chamber sheet-fed-type film formation apparatus MSL-464,manufactured by Tokki Corp.) to which a cryopump was connected. Filmthickness was controlled by regulating discharging time. Thus, theformation of the carbon diffusion prevention layer and the followingformation of the Al-alloy reflective layer and the carbon buffer layerwere performed by continuous film formation by means of sputtering.

The obtained Cu/C/Al-alloy/C electrode foil was subjected to heattreatment at 250° C. for 30 minutes under ambient atmosphere, in orderto evaluate existence/absence of thermal migration. The laminatecross-section of the Cu/C/Al-alloy in the heat-treated electrode foilwas observed by transmission electron microscope (TEM) to obtain amicrophotograph shown in FIG. 9A. In addition, the thickness of thecarbon diffusion prevention layer 63 was measured to be 1.7 nm. Energydispersive X-ray analysis (EDX) was conducted on point B on thecross-section of the Al-alloy reflective layer 64 and on point C on thecross-section of the copper foil 62 in the laminate cross-section shownin FIG. 9A to obtain spectra to shown in FIGS. 9B and 9C, respectively.It can be understood from comparison between FIGS. 9B and 9C that Cuderived from the copper foil was not diffused into the Al-alloyreflective layer, in other words, diffusion of Cu into the Al-alloyreflective layer (thermal migration) was prevented by the carbondiffusion prevention layer.

Example 7 Preparation and Heat-Resistance Evaluation ofCu/Cr—Ti/Al-alloy/C Electrode Foil

An electrode foil was prepared in the same manner as in Example 2 exceptthat a Cr—Ti layer was formed by sputtering as a diffusion preventionlayer between the copper foil and the Al-alloy reflective layer. Thissputtering for forming the Cr—Ti diffusion prevention layer wasperformed under the conditions of input power (DC) of 500 W (1.6 W/cm²);ultimate vacuum of lower than 5×10⁻⁵ Pa; sputtering pressure of 0.5 Pa;Ar flow rate of 100 sccm; and substrate temperature at room temperature,after mounting a Cr—Ti alloy target (203.2 mm diameter and 8 mm thick)having a composition of the weight ratio Cr:Ti=1:1 on a magnetronsputtering apparatus (Multi-chamber sheet-fed-type film formationapparatus MSL-464, manufactured by Tokki Corp.) to which a cryopump wasconnected. Film thickness was controlled by regulating discharging time.Thus, the formation of the Cr—Ti diffusion prevention layer and thefollowing formation of the Al-alloy reflective layer and the carbonbuffer layer were performed by continuous film formation by means ofsputtering.

The obtained Cu/Cr—Ti/Al-alloy/C electrode foil was subjected to heattreatment at 250° C. for 30 minutes under ambient atmosphere, in orderto evaluate existence/absence of thermal migration. The laminatecross-section of the Cu/Cr—Ti/Al-alloy in the heat-treated electrodefoil was observed by transmission electron microscope (TEM) to obtain amicrophotograph shown in FIG. 10A. In addition, the thickness of theCr—Ti diffusion prevention layer 73 was measured to be 20 nm. Energydispersive X-ray analysis (EDX) was conducted on point B on thecross-section of the Al-alloy reflective layer 74 and on point C on thecross-section of the copper foil 72 in the laminate cross-section shownin FIG. 10A to obtain spectra to shown in FIGS. 10B and 10C,respectively. It can be understood from comparison between FIGS. 10B and10C that Cu derived from the copper foil was not diffused into theAl-alloy reflective layer, in other words, diffusion of Cu into theAl-alloy reflective layer (thermal migration) was prevented by the Cr—Tidiffusion prevention layer.

Example 8 Heat-Resistance Evaluation of Cu/Al-alloy/C Electrode Foil

For comparison, heat-resistance evaluation was performed on theCu/Al-alloy/C electrode foil without diffusion prevention layer preparedin Example 2, in the same manner as in Examples 7 and 8. Specifically,the obtained Cu/Al-alloy/C electrode foil was subjected to heattreatment at 250° C. for 30 minutes under ambient atmosphere, in orderto evaluate existence/absence of thermal migration. The laminatecross-section of the Cu/Al-alloy in the heat-treated electrode foil wasobserved by transmission electron microscope (TEM) to obtain amicrophotograph shown in FIG. 11A. Energy dispersive X-ray analysis(EDX) was conducted on point B on the cross-section of the Al-alloyreflective layer 84 and on point C on the cross-section of the copperfoil 82 in the laminate cross-section shown in FIG. 11A to obtainspectra to shown in FIGS. 11B and 11C, respectively. It can beunderstood from comparison between FIGS. 11B and 11C that Cu derivedfrom the copper foil was diffused into the Al-alloy reflective layer toform a diffused layer with a thickness of about 100 nm, in other words,diffusion of Cu into the Al-alloy reflective layer (thermal migration)progressed in the absence of a diffusion prevention layer.

1. An electrode foil comprising: a metal foil; a diffusion preventionlayer for preventing diffusion of metal derived from the metal foil, thediffusion prevention layer being provided directly on the metal foil;and a reflective layer provided directly on the diffusion preventionlayer.
 2. The electrode foil according to claim 1 for use as an anode ora cathode in an organic EL element or an organic solar cell.
 3. Theelectrode foil according to claim 1, which is free from an insulatinglayer at least on or to the side of the reflective layer.
 4. Theelectrode foil according to claim 1, wherein an outermost surface on orto the side of the reflective layer is an ultra-smooth surface having anarithmetic average roughness Ra of 10.0 nm or less as measured inaccordance with JIS B 0601-2001.
 5. The electrode foil according toclaim 1, wherein the metal foil has a thickness of from 1 μm to 250 μm.6. The electrode foil according to claim 1, wherein the metal foil is anonmagnetic metal foil.
 7. The electrode foil according to claim 1,wherein the metal foil is a copper foil.
 8. The electrode foil accordingto claim 1, wherein the diffusion prevention layer is a layer comprisingat least one of Mo, Ti, Ta, Cr, W, Ni, Fe, Co, C, Zn, Li, Y, indiumoxide, tin oxide, zinc oxide, molybdenum oxide, gallium oxide, vanadiumoxide, tungsten oxide, ruthenium oxide, aluminum oxide, titanium oxide,titanium nitride, chromium nitride, tantalum nitride, NiP, Ni—Zn, LiF,MgF₂, CaF₃, NaAlF₆, and NaF₆.
 9. The electrode foil according to claim1, wherein the reflective layer is at least one selected from the groupconsisting of an aluminum film, an aluminum alloy film, a silver film,and a silver alloy film.
 10. The electrode foil according to claim 1,further comprising a transparent or translucent buffer layer directlyprovided on the reflective layer, wherein the surface of the bufferlayer constitutes the ultra-smooth surface.
 11. The electrode foilaccording to claim 9, wherein the buffer layer is at least one selectedfrom the group consisting of an conductive amorphous carbon film, anconductive oxide film, a magnesium alloy film, and a fluoride film. 12.The electrode foil according to claim 1, having a thickness of from 1 μmto 300 μm.
 13. The electrode foil according to claim 1, wherein asurface of the metal foil opposite to the reflective layer is aroughened surface having a ten-point average roughness Rz of 1.0 μm ormore as measured in accordance with JIS B 0601-1994.
 14. An organicdevice which is an organic EL element and/or an organic solar cell, theorganic device comprising: the electrode foil according to claim 1; anorganic semiconductor layer comprising an organic EL layer and/or anorganic solar cell active layer, the organic semiconductor layer beingprovided directly on an outermost surface on or to the side of thereflective layer of the electrode foil; and a transparent or translucentcounter electrode provided on the organic semiconductor layer.
 15. Theorganic device according to claim 14, wherein the counter electrodecomprises at least one selected from the group consisting of anconductive amorphous carbon film, an conductive oxide film, a magnesiumalloy film, and a fluoride film.
 16. An organic EL lighting comprisingthe organic device according to claim 14 as an organic EL element.